Inkjet ink composition and inkjet recording method

ABSTRACT

An inkjet ink composition is provided that includes (Component A) an N-vinyllactam, (Component B) a di(meth)acrylate ester of at least one type of diol selected from the group consisting of a straight-chain hydrocarbon diol having 9 to 18 carbon atoms, a branched hydrocarbon diol having 6 to 18 carbon atoms, and a monoalicyclic hydrocarbon diol having 6 to 18 carbon atoms, and (Component C) at least one type of polymerization initiator selected from the group consisting of an α-amino ketone compound, a thioxanthone compound, a thiochromanone compound, and a bisacylphosphine oxide compound. There is also provided an inkjet recording method that includes (a) an image formation step of forming an image above a support by discharging the inkjet ink composition by an inkjet method and (b) a curing step of curing the ink composition by irradiating the obtained image with actinic radiation to thus obtain a printed material having a cured image above the support.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inkjet ink composition and an inkjetrecording method.

2. Description of the Related Art

As image recording methods for forming an image on a recording mediumsuch as paper based on an image data signal, there are anelectrophotographic system, sublimation type and melt type thermaltransfer systems, an inkjet system, etc.

With regard to the inkjet system, the printing equipment is inexpensive,it is not necessary to use a plate when printing, and since an image isformed directly on a recording medium by discharging an ink compositiononly on a required image area, the ink composition can be usedefficiently and the running cost is low, particularly in the case ofsmall lot production. Furthermore, there is little noise and it isexcellent as an image recording system, and has been attractingattention in recent years.

Among them, an inkjet recording ink composition (radiation-curing inkjetrecording ink composition), which is curable upon exposure to radiationsuch as UV rays, is an excellent system from the viewpoint of it beingpossible to print on various types of recording media because, comparedwith a solvent-based ink composition, the drying properties areexcellent and an image is resistant to spreading since the majority ofthe components in the ink composition cure upon exposure to radiationsuch as UV rays. Examples of conventional ink composition for inkjetrecording are described in JP-A-2007-262178 (JP-A denotes a Japaneseunexamined patent application publication) and International PatentApplication WO 2007/55333.

BRIEF SUMMARY OF THE INVENTION Problems to be Solved by the Invention

It is an object of the present invention to provide an inkjet inkcomposition that has excellent curability and gives an image free fromstripe unevenness and having excellent surface gloss and flexibility,and an inkjet recording method that has excellent curability and givesan image free from stripe unevenness and having excellent surface glossand flexibility.

The above-mentioned object has been accomplished by means described in<1> or <14> below. They are shown below together with <2> to <13> and<15>, which are preferred embodiments.

<1> An inkjet ink composition comprising (Component A) an N-vinyllactam,(Component B) a di(meth)acrylate ester of at least one type of diolselected from the group consisting of a straight-chain hydrocarbon diolhaving 9 to 18 carbon atoms, a branched hydrocarbon diol having 6 to 18carbon atoms, and a monoalicyclic hydrocarbon diol having 6 to 18 carbonatoms, and (Component C) at least one type of polymerization initiatorselected from the group consisting of an α-amino ketone compound, athioxanthone compound, a thiochromanone compound, and a bisacylphosphineoxide compound,<2> the inkjet ink composition according to <1> above, wherein ComponentB above is a di(meth)acrylate ester of at least one type of diolselected from the group consisting of a straight-chain hydrocarbon diolhaving 10 to 18 carbon atoms, a branched hydrocarbon diol having 6 to 18carbon atoms, and a monoalicyclic hydrocarbon diol having 6 to 18 carbonatoms,<3> the inkjet ink composition according to <1> or <2> above, whereinComponent B above is a di(meth)acrylate ester of at least one type ofdiol selected from the group consisting of a branched hydrocarbon diolhaving 6 to 18 carbon atoms and a monoalicyclic hydrocarbon diol having6 to 18 carbon atoms,<4> the inkjet ink composition according to <2> above, wherein ComponentB above is at least one di(meth)acrylate ester selected from the groupconsisting of 1,10-decanediol diacrylate, 1,12-dodecanediol diacrylate,3-methyl-1,5-pentanediol diacrylate, and cyclohexanedimethanoldiacrylate, <5> the inkjet ink composition according to <3> above,wherein Component B above is at least one di(meth)acrylate esterselected from the group consisting of 3-methyl-1,5-pentanedioldiacrylate and cyclohexanedimethanol diacrylate,<6> the inkjet ink composition according to any one of <1> to <5> above,wherein Component B above comprises 3-methyl-1,5-pentanediol diacrylate,<7> the inkjet ink composition according to any one of <1> to <6> above,wherein it further comprises (Component D) a compound represented byFormula (D),

(In Formula (D), R¹ denotes a hydrogen atom or a methyl group and R² toR¹² independently denote a hydrogen atom or an alkyl group.)<<8> the inkjet ink composition according to <7> above, wherein ComponentD above comprises 4-t-butylcyclohexyl (meth)acrylate and/or3,3,5-trimethylcyclohexyl (meth)acrylate,<9> the inkjet ink composition according to any one of <1> to <8> above,wherein Component B above has a content of at least 15 wt % but nogreater than 50 wt % relative to the total weight of the inkcomposition,<10> the inkjet ink composition according to any one of <1> to <9>above, wherein Component A above has a content of at least 8 wt % but nogreater than 35 wt % relative to the total weight of the inkcomposition,<11> the inkjet ink composition according to any one of <1> to <10>above, wherein it comprises at least three types of polymerizationinitiators selected from the group consisting of an α-amino ketonecompound, a thioxanthone compound, a thiochromanone compound, abisacylphosphine oxide compound, an α-hydroxy ketone compound, and amonoacylphosphine oxide compound,<12> the inkjet ink composition according to any one of <1> to <11>above, wherein it comprises neither a silicone-based surfactant nor afluorine-based surfactant or comprises a total content of silicone-basedand fluorine-based surfactants of greater than 0 wt % but no greaterthan 0.1 wt % relative to the total weight of the ink composition,<13> the inkjet ink composition according to any one of <1> to <12>above, wherein of ethylenically unsaturated compounds contained in theink composition, at least 75 wt % are compounds having no ether bond,<14> an inkjet recording method comprising (a) an image formation stepof forming an image above a support by discharging the inkjet inkcomposition according to any one of <1> to <13> above by an inkjetmethod and (b) a curing step of curing the ink composition byirradiating the obtained image with actinic radiation to thus obtain aprinted material having a cured image above the support, and<15> the inkjet recording method according to <14> above, wherein atleast part of the image in the printed material is formed by repeatingthe image formation step and the curing step two or more times.

Inkjet Ink Composition

The inkjet ink composition of the present invention (hereinafter, alsocalled the ‘ink composition’) comprises (Component A) an N-vinyllactam,(Component B) a di(meth)acrylate ester of at least one type of diolselected from the group consisting of a straight-chain hydrocarbon diolhaving 9 to 18 carbon atoms, a branched hydrocarbon diol having 6 to 18carbon atoms, and a monoalicyclic hydrocarbon diol having 6 to 18 carbonatoms, and (Component C) at least one type of polymerization initiatorselected from the group consisting of an α-amino ketone, a thioxanthonecompound, a thiochromanone compound, and a bisacylphosphine oxidecompound.

In the present specification, ‘A to B’, which expresses a numericalrange, has the same meaning as ‘at least A but no greater than B’.Furthermore, ‘(Component A) an N-vinyllactam’ is also called simply‘Component A’.

The ink composition of the present invention is an oil-based inkcomposition that is curable upon exposure to actinic radiation.

The ‘actinic radiation’ referred to in the present invention isradiation that can provide energy that enables an initiating species tobe generated in the ink composition when irradiated, includes a rays, grays, X rays, ultraviolet rays, visible light, and an electron beam.Among these, ultraviolet rays and an electron beam are preferable fromthe viewpoint of curing sensitivity and the availability of equipment,and ultraviolet rays are more preferable.

It is said that, compared with a printed material obtained by aqueousinkjet printing or solvent inkjet printing, in the case of a printedmaterial obtained by actinic radiation-curing type inkjet printing acured film has low surface gloss and marked stripe unevenness. It isthought that one of main causes therefor is the shape of a fired dropletwhen landing being retained since the fired droplet is cured by actinicradiation immediately after landing of the inkjet.

On the other hand, the ink composition of the present invention gives aninkjet image that has excellent printed material surface gloss andlittle stripe unevenness. Although the reason therefor is not certain,it is thought that the discharged ink composition comprising Component Ato Component C cures from an inner part of a fired droplet byirradiation with actinic radiation immediately after landing. On theother hand, by the effect of Component B in particular, which isexpected to have a high dissolved oxygen content, only the fired dropletoutermost surface, which is in contact with the air, is selectivelysubjected to oxygen polymerization inhibition, the outermost surface ofthe fired droplet is kept in a liquid state for a long period of time,the fired droplet outermost surface spreads while wet, and coalescing ispromoted. It is surmised that, as a result, a smoother level surface isformed and an image having a high degree of surface gloss and littlestripe unevenness is obtained. When printing in a multipass mode inwhich the same area is printed by overstriking, there is a case in whicha fired droplet is overlayered on a previously fired liquid dropletduring overstriking. In this process, it is thought that if theoutermost surface of the ink film of the previously fired droplet is ina liquid state, the degree of spreading while wet of the subsequentlyfired droplet increases, and higher surface gloss is obtained.

When controlling the cured state of a fired droplet, it is important tomaintain only the very outermost surface of the fired droplet in aliquid state. If the interior of the fired droplet is kept in a liquidstate for a long period of time, a final printed material might becometacky, or a subsequently fired droplet might enter the film interiorwhen overstriking, thus forming a crater-like recess in a printedmaterial. As a result, the smoothness of a printed material surfacemight be undesirably lost. Furthermore, it is thought that lowcurability of the interior might cause interference between fireddroplets (the position of fired droplets being displaced due tooverlapping of the fired droplets), thus accentuating stripe unevenness.

It is though that, in accordance with the present invention, since thecombination of Component A to Component C makes it possible toselectively maintain only the cured film outermost surface in a liquidstate for a long period of time while strongly promoting the curabilityof the interior of a fired droplet, a printed material having highsurface gloss and little stripe unevenness is obtained.

(Component A) N-vinylcaprolactam

The ink composition of the present invention comprises (Component A)N-vinylcaprolactam. Component A is preferably a compound represented byFormula (A).

In Formula (A), n denotes an integer of 2 to 6; n is preferably aninteger of 3 to 5 from the viewpoint of flexibility after the inkcomposition is cured, adhesion to a recording medium, and readyavailability of starting materials, n is more preferably 3 or 5, and nis particularly preferably 5, which is N-vinylcaprolactam.N-vinylcaprolactam is preferable since it has excellent safety, iscommonly used and is readily available at a relatively low price, andgives particularly good ink curability and adhesion of a cured film to arecording medium.

The N-vinyllactam may have a substituent such as an alkyl group or anaryl group on the lactam ring, and may have a saturated or unsaturatedring structure bonded to the lactam ring.

Component A May be Used Singly or in a Combination of Two or MoreCompounds.

The content of Component A is, relative to the total weight of the inkcomposition, preferably 8 to 40 wt %, more preferably 8 to 35 wt %, yetmore preferably 12 to 32 wt %, and particularly preferably 14 to 25 wt%. When in the above-mentioned range, the cured film outermost surfacealone can be selectively maintained in a liquid state for a long periodof time while strongly promoting the curability of the interior of theimage, and a printed material having high surface gloss and littlestripe unevenness is obtained.

(Component B) Di(Meth)Acrylate Ester of at Least One Type of DiolSelected from The Group Consisting of Straight-Chain Hydrocarbon DiolHaving 9 to 18 Carbon Atoms, Branched Hydrocarbon Diol Having 6 to 18Carbon Atoms, and Monoalicyclic Hydrocarbon Diol Having 6 to 18 CarbonAtoms

The ink composition of the present invention comprises (Component B) adi(meth)acrylate ester of at least one type of diol selected from thegroup consisting of a straight-chain hydrocarbon diol having 9 to 18carbon atoms, a branched hydrocarbon diol having 6 to 18 carbon atoms,and a monoalicyclic hydrocarbon diol having 6 to 18 carbon atoms.

From the viewpoint of surface gloss, Component B is preferably adi(meth)acrylate ester of at least one type of diol selected from thegroup consisting of a straight-chain hydrocarbon diol having 10 to 18carbon atoms, a branched hydrocarbon diol having 6 to 18 carbon atoms,and a monoalicyclic hydrocarbon diol having 6 to 18 carbon atoms, morepreferably a di(meth)acrylate ester of at least one type of diolselected from the group consisting of a branched hydrocarbon diol having6 to 18 carbon atoms and a monoalicyclic hydrocarbon diol having 6 to 18carbon atoms, and yet more preferably a di(meth)acrylate ester of abranched hydrocarbon diol having 6 to 18 carbon atoms.

The number of carbon atoms of the straight-chain hydrocarbon diol ispreferably 10 to 18, more preferably 10 to 16, and yet more preferably10 to 12.

The straight-chain hydrocarbon diol preferably does not contain anunsaturated bond.

Examples of the di(meth)acrylate ester of a straight-chain hydrocarbondiol having 9 to 18 carbon atoms include nonanediol di(meth)acrylate,decanediol di(meth)acrylate, dodecanediol di(meth)acrylate,tridecanediol di(meth)acrylate, and octadecanediol di(meth)acrylate.Among them, an acrylate compound is preferable, decanediol diacrylate ordodecanediol diacrylate is more preferable, and decanediol diacrylate isparticularly preferable.

The number of carbon atoms of the branched hydrocarbon diol ispreferably 6 to 12, and more preferably 6 to 8.

The branched hydrocarbon diol preferably does not contain an unsaturatedbond. The number of carbon atoms of the straight-chain connecting thehydroxy groups in the branched hydrocarbon diol is preferably 3 to 5.The alkyl group branching from the straight-chain preferably has 1 to 4carbon atoms, and is more preferably a methyl group. The number ofbranches is preferably 1 or 2, and more preferably 1.

Preferred examples of the di(meth)acrylate ester of a branchedhydrocarbon diol having 6 to 18 carbon atoms include3-methyl-1,5-pentanediol di(meth)acrylate and2-n-butyl-2-ethyl-1,3-propanediol diacrylate; 3-methyl-1,5-pentanedioldiacrylate is more preferable.

The monoalicyclic hydrocarbon diol is an aliphatic hydrocarbon compoundhaving two hydroxy groups and only one hydrocarbon ring, and is acompound that does not have an aromatic ring, a bridged ring, a fusedring, etc.

The number of carbon atoms of the monocyclic hydrocarbon diol ispreferably 6 to 12, and more preferably 6 to 10.

The monoalicyclic hydrocarbon diol preferably does not contain anunsaturated bond. The number of carbon atoms forming the ring in themonocyclic hydrocarbon diol is preferably 3 to 12, more preferably 4 to10, and yet more preferably 5 to 8.

The hydroxy groups and the ring of the cyclic hydrocarbon diol may bebonded directly or via a linking group. The linking group is preferablyan alkylene group having 1 to 5 carbon atoms, more preferably analkylene group having 1 to 3 carbon atoms, and yet more preferably amethylene group.

Examples of the di(meth)acrylate ester of a monoalicyclic hydrocarbondiol having 6 to 18 carbon atoms include cyclohexanedimethanoldi(meth)acrylate and cyclohexanediol di(meth)acrylate. Among them,cyclohexanedimethanol di(meth)acrylate is preferable, andcyclohexanedimethanol diacrylate is more preferable.

From the viewpoint of curability and flexibility, the content ofComponent B relative to the total weight of the ink composition ispreferably 10 to 60 wt %, more preferably 15 to 55 wt %, yet morepreferably 15 to 50 wt %, and particularly preferably 20 to 45 wt %.

From the viewpoint of improvement of surface gloss and suppression ofstripe unevenness, the total content of Component A and Component B inthe ink composition of the present invention relative to the totalweight of the ink composition is preferably at least 30 wt %, morepreferably 35 to 95 wt %, and yet more preferably 40 to 90 wt %.

From the viewpoint of improvement of surface gloss and suppression ofstripe unevenness, the total content of Component A and Component B inthe polymerizable compounds in the ink composition of the presentinvention relative to the total weight of the polymerizable compounds ispreferably at least 70 wt %, more preferably 75 to 98 wt %, and yet morepreferably 80 to 95 wt %.

(Component C) at Least One Type of Polymerization Initiator Selectedfrom the Group Consisting of α-Amino Ketone, Thioxanthone Compound,Thiochromanone Compound, and Bisacylphosphine Oxide Compound

The ink composition of the present invention comprises (Component C) atleast one type of polymerization initiator selected from the groupconsisting of an α-amino ketone compound, a thioxanthone compound, athiochromanone compound, and a bisacylphosphine oxide compound. Due toComponent C being contained, the ink composition of the presentinvention has excellent curability and can give an image with suppressedstripe unevenness.

Furthermore, from the viewpoint of surface gloss it is preferable forthe ink composition of the present invention to comprise at least threetypes of polymerization initiators selected from the group consisting ofan α-amino ketone, a thioxanthone compound, a thiochromanone compound, abisacylphosphine oxide compound, an α-hydroxy ketone compound, and amonoacylphosphine oxide compound, it is more preferable for it tocomprise an α-amino ketone compound, a bisacylphosphine oxide compound,and a thioxanthone compound or a thiochromanone compound or comprise anα-hydroxy ketone compound, a monoacylphosphine oxide compound, and athioxanthone compound or a thiochromanone compound, and it isparticularly preferable for it to comprise an α-amino ketone compound, abisacylphosphine oxide compound, and a thioxanthone compound or athiochromanone compound.

Furthermore, the ink composition of the present invention preferablycomprises a thioxanthone compound and/or a thiochromanone compound; morepreferably a thioxanthone compound from the viewpoint of cost, and morepreferably a thiochromanone compound from the viewpoint of transparency.

The α-amino ketone compound is not particularly limited; a knowncompound may be used, and a compound represented by Formula (C-1) belowis preferable.

In Formula (C-1) above, Ar denotes a phenyl group that is substitutedwith —SR¹³ or —N(R^(7E))(R^(8E)), R¹³ denotes a hydrogen atom or analkyl group, R^(1D) and R^(2D) independently denote an alkyl grouphaving 1 to 8 carbon atoms, and R^(3D) and R^(4D) independently denote ahydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkylgroup having 2 to 4 carbon atoms substituted with an alkoxy group having1 to 4 carbon atoms, or an alkenyl group having 3 to 5 carbon atoms.R^(1D) and R^(2D) may be bonded to each other to form an alkylene grouphaving 2 to 9 carbon atoms. R^(3D) and R^(4D) may be bonded to eachother to form an alkylene group having 3 to 7 carbon atoms, and thealkylene group may contain —O— or —N(R¹²)— in an alkylene chain. R¹²denotes an alkyl group having 1 to 4 carbon atoms. R^(7E) and R^(8E)independently denote a hydrogen atom, an alkyl group having 1 to 12carbon atoms, an alkyl group having 2 to 4 carbon atoms substituted withan alkoxy group having 1 to 4 carbon atoms, or an alkenyl group having 3to 5 carbon atoms. R^(7E) and R^(8E) may be bonded to each other to forman alkylene group having 3 to 7 carbon atoms, and the alkylene group maycontain —O— or —N(R¹²)— in an alkylene chain. Here, R¹² has the samemeaning as above.

Examples of the α-amino ketone compound include2-methyl-1-phenyl-2-morpholinopropan-1-one,2-methyl-1-[4-(hexyl)phenyl]-2-morpholinopropan-1-one, and2-ethyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one. Furthermore,a commercial product such as IRGACURE 907, IRGACURE 369, or IRGACURE 379manufactured by Ciba-Geigy Ltd. can be cited as a preferred example.

The thioxanthone compound is not particularly limited; a known compoundmay be used, and a compound represented by Formula (C-2) below ispreferable.

In Formula (C-2) above, R^(1F), R^(2F), R^(3F), R^(4F), R^(5F), R^(6F),R^(7F), and R^(8F) independently denote a hydrogen atom, an alkyl group,a halogen atom, a hydroxy group, a cyano group, a nitro group, an aminogroup, an alkylthio group, an alkylamino group (The alkylamino groupincludes the case of monoalkylsubstituted amino group anddialkylsubstituted amino group. It is same also in the following.), analkoxy group, an alkoxycarbonyl group, an acyloxy group, an acyl group,a carboxy group, or a sulfo group. The number of carbon atoms of analkyl moiety in the alkyl group, alkylthio group, alkylamino group,alkoxy group, alkoxycarbonyl group, acyloxy group, and acyl group ispreferably 1 to 20, more preferably 1 to 8, and yet more preferably 1 to4.

Two of R^(1F), R^(2F), R^(3F), R^(4F), R^(5F), R^(6F), R^(7F), andR^(8F) that are adjacent may be joined to each other to form a ring.When they form a ring, examples of the ring structure include a 5- or6-membered aliphatic or aromatic ring; it may be a heterocyclic ringcontaining an element other than a carbon atom, and rings thus formedmay be further combined to form a bicyclic ring, for example a fusedring. These ring structures may further have a substituent. Examples ofthe substituent include a halogen atom, a hydroxy group, a cyano group,a nitro group, an amino group, an alkylthio group, an alkylamino group,an alkoxy group, an alkoxycarbonyl group, an acyloxy group, an acylgroup, a carboxy group, and a sulfo group. Examples of a heteroatom whenthe resulting ring structure is a heterocyclic ring include N, O, and S.

Examples of the thioxanthone compound include thioxanthone,2-isopropylthioxanthone, 2-chlorothioxanthone, 2-dodecylthioxanthone,2,4-diethylthioxanthone, 2,4-dimethylthioxanthone,1-methoxycarbonylthioxanthone, 2-ethoxycarbonylthioxanthone,3-(2-methoxyethoxycarbonyl)thioxanthone, 4-butoxycarbonylthioxanthone,3-butoxycarbonyl-7-methylthioxanthone, 1-cyano-3-chlorothioxanthone,1-ethoxycarbonyl-3-chlorothioxanthone,1-ethoxycarbonyl-3-ethoxythioxanthone,1-ethoxycarbonyl-3-aminothioxanthone,1-ethoxycarbonyl-3-phenylsulfurylthioxanthone, 3,4-di[2-(2-methoxyethoxy)ethoxycarbonyl]thioxanthone,1-ethoxycarbonyl-3-(1-methyl-1-morpholinoethyl)thioxanthone,2-methyl-6-dimethoxymethylthioxanthone,2-methyl-6-(1,1-dimethoxybenzyl)thioxanthone,2-morpholinomethylthioxanthone, 2-methyl-6-morpholinomethylthioxanthone,n-allylthioxanthone-3,4-dicarboximide,n-octylthioxanthone-3,4-dicarboxylmide,N-(1,1,3,3-tetramethylbutyl)thioxanthone-3,4-dicarboxylmide,1-phenoxythioxanthone, 6-ethoxycarbonyl-2-methoxythioxanthone,6-ethoxycarbonyl-2-methylthioxanthone, thioxanthone-2-polyethyleneglycol ester, and2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthon-2-yloxy)-N,N,N-trimethyl-1-propanaminiumchloride. Among them, from the viewpoint of ready availability andcurability, thioxanthone, 2-isopropylthioxanthone,4-isopropylthioxanthone, 2,3-diethylthioxanthone,2,4-diethylthioxanthone, 2,4-dichlorothioxanthone,1-chloro-4-propoxythioxanthone, 2-cyclohexylthioxanthone,4-cyclohexylthioxanthone, 2-isopropylthioxanthone, and4-isopropylthioxanthone are preferable, and 2-isopropylthioxanthone and4-isopropylthioxanthone are more preferable.

The thiochromanone compound is not particularly limited; a knowncompound may be used, and a compound represented by Formula (C-3) belowis preferable.

In Formula (C-3), R^(1G), R^(2G), R^(3G), R^(4G), R^(5G), R^(6G),R^(7G), and R^(8G) independently denote a hydrogen atom, an alkyl group,a halogen atom, a hydroxy group, a cyano group, a nitro group, an aminogroup, an alkylthio group, an alkylamino group, an alkoxy group, analkoxycarbonyl group, an acyloxy group, an acyl group, a carboxy group,or a sulfo group. The number of carbon atoms of an alkyl moiety of thealkyl group, alkylthio group, alkylamino group, alkoxy group,alkoxycarbonyl group, acyloxy group, and acyl group is preferably 1 to20, more preferably 1 to 8, and yet more preferably 1 to 4.

Two of R^(1G), R^(2G), R^(3G), and R^(4G) that are adjacent may bebonded to each other, for example fused, to form a ring.

Examples of the ring structure when those above form a ring include a 5or 6-membered aliphatic ring or aromatic ring; it may be a heterocyclicring containing an element other than a carbon atom, and rings thusformed may be further combined to form a bicyclic ring, for example afused ring. These ring structures may further have a substituent.Examples of the substituent include those described for Formula (C-2).Examples of a heteroatom when the resulting ring structure is aheterocyclic ring include N, O, and S.

Furthermore, the thiochromanone compound is preferably a compound havingon the thiochromanone ring structure at least one substituent (an alkylgroup, a halogen atom, a hydroxy group, a cyano group, a nitro group, anamino group, an alkylthio group, an alkylamino group, an alkoxy group,an alkoxycarbonyl group, an acyloxy group, an acyl group, a carboxygroup, a sulfo group, etc.). As examples of the substituent above, analkyl group, a halogen atom, a hydroxy group, an alkylthio group, analkylamino group, and an acyloxy group are preferable, an alkyl group,and a halogen atom having 1 to 20 carbon atoms are more preferable, analkyl group, and a halogen atom having 1 to 4 carbon atoms are yet morepreferable.

The thiochromanone compound is preferably a compound having at least onesubstituent on an aromatic ring and at least one substituent on thethiochromanone ring structure.

The specific examples of the thiochromanone compound preferably include(I-1) to (I-31) listed below. Among them, (I-14), (I-17) and (I-19) ismore preferable, and (I-14) is particularly preferable.

The bisacylphosphine oxide compound is not particularly limited; a knowncompound may be used, and a compound represented by Formula (C-4) belowis preferable.

(In Formula (C-4), R^(1H), R^(2H), and R^(3H) independently denote anaromatic hydrocarbon group that may have a methyl group or an ethylgroup as a substituent.)

As the bisacylphosphine oxide compound, a known bisacylphosphine oxidecompound may be used. Examples thereof include bisacylphosphine oxidecompounds described in JP-A-3-101686, JP-A-5-345790, and JP-A-6-298818.

Specific examples thereof includebis(2,6-dichlorobenzoyl)phenylphosphine oxide,bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide,bis(2,6-dichlorobenzoyl)-4-ethoxyphenylphosphine oxide,bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide,bis(2,6-dichlorobenzoyl)-2-naphthylphosphine oxide,bis(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide,bis(2,6-dichlorobenzoyl)-4-chlorophenylphosphine oxide,bis(2,6-dichlorobenzoyl)-2,4-dimethoxyphenylphosphine oxide,bis(2,6-dichlorobenzoyl)decylphosphine oxide,bis(2,6-dichlorobenzoyl)-4-octylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2,5-dimethylphenylphosphine oxide,bis(2,6-dichloro-3,4,5-trimethoxybenzoyl)-2,5-dimethylphenylphosphineoxide, bis(2,6-dichloro-3,4,5-trimethoxybenzoyl)-4-ethoxyphenylphosphineoxide, bis(2-methyl-1-naphthoyl)-2,5-dimethylphenylphosphine oxide,bis(2-methyl-1-naphthoyl)-4-ethoxyphenylphosphine oxide,bis(2-methyl-1-naphthoyl)-2-naphthylphosphine oxide,bis(2-methyl-1-naphthoyl)-4-propylphenylphosphine oxide,bis(2-methyl-1-naphthoyl)-2,5-dimethylphenylphosphine oxide,bis(2-methoxy-1-naphthoyl)-4-ethoxyphenylphosphine oxide,bis(2-chloro-1-naphthoyl)-2,5-dimethylphenylphosphine oxide, andbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

Among them, the bisacylphosphine oxide compound is preferablybis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (IRGACURE 819: CibaSpecialty Chemicals),bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphenylphosphine oxide,etc.

In the present invention, from the viewpoint of curability anduniformity of the degree of curing within a cured film, the total amountof Component C used relative to the total content of polymerizablecompounds including Component A and Component B is preferably in therange of 0.01 to 35 wt %, more preferably 0.5 to 20 wt %, and yet morepreferably 1.0 to 15 wt %.

Furthermore, when a thioxanthone compound and/or a thiochromanonecompound are used, the total content I of polymerization initiatorsother than the thioxanthone compound and the thiochromanone compoundrelative to the total content S of the thioxanthone compound and/or thethiochromanone compound is preferably I:S=200:1 to 1:200 as a ratio byweight, more preferably 50:1 to 1:50, and yet more preferably 20:1 to1:5.

From the viewpoint of improvement of surface gloss and suppression ofstripe unevenness, the total content of Component A to Component C inthe ink composition of the present invention relative to the totalweight of the ink composition is preferably at least 50 wt %, morepreferably 60 to 98 wt %, and yet more preferably 70 to 95 wt %.

(Component D) Compound represented by Formula (D)

From the viewpoint of surface gloss, the ink composition of the presentinvention preferably comprises (Component D) a compound represented byFormula (D).

(In Formula (D), R¹ denotes a hydrogen atom or a methyl group, and R² toR¹² independently denote a hydrogen atom or an alkyl group.)

R¹ denotes a hydrogen atom or a methyl group, and from the viewpoint ofcurability is preferably a hydrogen atom.

R² to R¹² independently denote a hydrogen atom or an alkyl group. Thealkyl group is preferably a straight-chain or branched alkyl grouphaving 1 to 10 carbon atoms, more preferably a straight-chain orbranched alkyl group having 1 to 6 carbon atoms, and yet more preferablya methyl group or a t-butyl group. It is preferable that at least one ofR² to R¹² is an alkyl group, it is more preferable that 1 to 5 thereofare alkyl groups, and it is yet more preferable that 1 to 3 thereof arealkyl groups.

Specific examples of Component D include 4-t-butylcyclohexyl(meth)acrylate, cyclohexyl (meth)acrylate, and trimethylcyclohexyl(meth)acrylate. Among them, 4-t-butylcyclohexyl (meth)acrylate and/or3,3,5-trimethylcyclohexyl (meth)acrylate are preferable, and4-t-butylcyclohexyl acrylate and/or 3,3,5-trimethylcyclohexyl acrylateare more preferable.

From the viewpoint of surface gloss, the content of. Component Drelative to the total weight of the ink composition is preferably 5 to45 wt %, more preferably 10 to 40 wt %, and yet more preferably 15 to 35wt %.

Other Polymerizable Compound

The ink composition of the present invention may comprise apolymerizable compound other than Component A, Component B, andComponent D. As the other polymerizable compound, an ethylenicallyunsaturated compound is preferable.

As the other polymerizable compound, a known polymerizable compound maybe used, and examples thereof include a (meth)acrylate compound otherthan Component A, Component B, and Component D, a vinyl ether compound,an allyl compound, an N-vinyl compound, and an unsaturated carboxylicacid. Examples thereof include radically polymerizable monomersdescribed in JP-A-2009-221414, polymerizable compounds described inJP-A-2009-209289, and ethylenically unsaturated compounds described inJP-A-2009-191183. Specific preferred examples of the other polymerizablecompound include phenoxyethyl (meth)acrylate and propylene oxide(PO)-modified neopentyl glycol di(meth)acrylate.

When a polymerizable compound other than Component A, Component B, andComponent D is added, from the viewpoint of curability and suppressionof image stripe unevenness it is preferable for the ink composition ofthe present invention to contain as little as possible of apolymerizable compound having an ether bond (ethereal oxygen atom). Thatis, the proportion of polymerizable compounds having no ether bond inthe ink composition of the present invention is, relative to the totalweight of the polymerizable compounds, preferably 55 to 100 wt %, morepreferably 65 to 100 wt %, and yet more preferably 75 to 100 wt %.

From the viewpoint of improvement of the surface gloss of a printedmaterial it is also preferable for the ink composition of the presentinvention to further comprise a (meth)acrylate ester of a straight-chainhydrocarbon monoalcohol having 8 to 18 carbon atoms as the otherpolymerizable compound. It is more preferably a (meth)acrylate ester ofa straight-chain hydrocarbon monoalcohol having 10 to 18 carbon atoms,and yet more preferably a (meth)acrylate ester of a straight-chainhydrocarbon monoalcohol having 10 to 13 carbon atoms.

Preferred examples of the (meth)acrylate ester of a straight-chainhydrocarbon monoalcohol having 8 to 18 carbon atoms include octyl(meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl(meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, andoctadecyl (meth)acrylate, and more preferred examples thereof includedecyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate,and tridecyl (meth)acrylate.

The content of the (meth)acrylate ester of a straight-chain hydrocarbonmonoalcohol having 8 to 18 carbon atoms relative to the total weight ofthe ink composition is preferably at least 5 wt % but no greater than 30wt %, more preferably at least 5 wt % but no greater than 25 wt %, yetmore preferably at least 5 wt % but no greater than 20 wt %, andparticularly preferably at least 5 wt % but no greater than 15 wt %.When in the above-mentioned range, an ink composition that gives a curedfilm having little tackiness and a printed material having excellentsurface gloss is obtained.

Furthermore, from the viewpoint of improvement of printed materialsurface gloss and suppression of the tackiness of a cured printedmaterial it is preferable for the ink composition of the presentinvention to comprise as the other polymerizable compound adi(meth)acrylate ester of a polyalicyclic hydrocarbon diol having 6 to18 carbon atoms.

Preferred examples of the di(meth)acrylate ester of a polyalicyclichydrocarbon diol having 6 to 18 carbon atoms includetricyclodecanedimethanol diacrylate.

The content of the di(meth)acrylate ester of a polyalicyclic hydrocarbondiol having 6 to 18 carbon atoms relative to the total weight of the inkcomposition is preferably at least 3 wt % but no greater than 25 wt %,more preferably at least 5 wt % but no greater than 20 wt %, and yetmore preferably at least 5 wt % but no greater than 15 wt %. When in theabove-mentioned range, an ink composition that has low viscosity andgives a cured film having little tackiness and a printed material havingexcellent surface gloss is obtained.

Furthermore, from the viewpoint of improvement of the surface gloss of aprinted material and suppression of the tackiness of a cured printedmaterial, it is more preferable to use in combination a (meth)acrylateester of a straight-chain hydrocarbon monoalcohol having 8 to 18 carbonatoms and a di(meth)acrylate ester of a polyalicyclic hydrocarbon diolhaving 6 to 18 carbon atoms. When used in combination as above, theratio by weight of the (meth)acrylate esters of a straight-chainhydrocarbon monoalcohol having 8 to 18 carbon atoms and the(meth)acrylate esters of a polyalicyclic hydrocarbon diol having 6 to 18carbon atoms is preferably 1:2 to 4:1, and more preferably 1:2 to 3:1.

Other Polymerization Initiator

The ink composition of the present invention may comprise apolymerization initiator other than Component C.

A polymerization initiator is a compound that absorbs external energysuch as the above-mentioned actinic radiation to thus form apolymerization-initiating species. With regard to the polymerizationinitiator, one type thereof may be used on its own or two or more typesthereof may be used in combination.

Preferred examples of the other polymerization initiator that can beused in the present invention include a radical polymerizationinitiator, and more preferred examples thereof include an α-hydroxyketone compound, a monoacylphosphine compound, an aromatic onium saltcompound, an organic peroxide, a thio compound, a hexaarylbiimidazolecompound, a ketoxime ester compound, a borate compound, an aziniumcompound, a metallocene compound, an active ester compound, and acompound having a carbon-halogen bond. Specific examples of thepolymerization initiator include radical polymerization initiatorsdescribed in JP-A-2008-208190. Among them, as the other polymerizationinitiator an α-hydroxy ketone compound and an acylphosphine compound canpreferably be cited.

Furthermore, the ink composition of the present invention may employ aknown sensitizer other than a thioxanthone compound or a thiochromanonecompound as the other polymerization initiator, but preferably does notcontain one. Examples of the sensitizer include those described inJP-A-2008-208190.

Examples of the α-hydroxy ketone compound include1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one,2-hydroxy-2-methyl-1-phenylpropan-1-one, and 1-hydroxycyclohexyl phenylketone; among them, a 1-hydroxycyclohexyl phenyl ketone compound ispreferable. In the present invention, the 1-hydroxycyclohexyl phenylketone compound includes a compound in which 1-hydroxycyclohexyl phenylketone is substituted with any substituent. The substituent may beselected freely as long as capability as a radical polymerizationinitiator is exhibited, and specific examples include an alkyl grouphaving 1 to 4 carbon atoms.

Examples of the monoacylphosphine oxide compound include methylisobutyrylmethylphosphinate, methyl isobutyrylphenylphosphinate, methylpivaloylphenylphosphinate, methyl 2-ethylhexanoylphenylphosphinate,isopropyl pivaloylphenylphosphinate, methyl p-toluoylphenylphosphinate,methyl o-toluoylphenylphosphinate, methyl2,4-dimethylbenzoylphenylphosphinate, isopropylp-t-butylbenzoylphenylphosphinate, methyl acryloylphenylphosphinate,isobutyryldiphenylphosphine oxide, 2-ethylhexanoyldiphenylphosphineoxide, o-toluoyldiphenylphosphine oxide,p-t-butylbenzoyldiphenylphosphine oxide,3-pyridylcarbonyldiphenylphosphine oxide, acryloyldiphenylphosphineoxide, benzoyldiphenylphosphine oxide, vinyl pivaloylphenylphosphinate,adipoylbisdiphenylphosphine oxide, pivaloyldiphenylphosphine oxide,p-toluoyld iphenylphosphine oxide, 4-(t-butyl)benzoyldiphenylphosphineoxide, terephthaloylbisdiphenylphosphine oxide,2-methylbenzoyldiphenylphosphine oxide, versatoyldiphenylphosphineoxide, 2-methyl-2-ethylhexanoyldiphenylphosphine oxide,1-methylcyclohexanoyldiphenylphosphine oxide, methylpivaloylphenylphosphinate, isopropyl pivaloylphenylphosphinate, and2,4,6-trimethylbenzoyldiphenylphosphine oxide. Among them,2,4,6-trimethylbenzoyldiphenylphosphine oxide is preferable.

In the present invention, when a polymerization initiator other thanComponent C is used, the amount thereof used relative to the totalcontent of the polymerizable compounds is preferably 0.01 to 20 wt %,and more preferably 0.5 to 15 wt %.

(Component E) Surfactant

The ink composition of the present invention may have a surfactant addedfor imparting stable discharge properties over a long period of time.

From the viewpoint of surface gloss and suppression of stripeunevenness, it is preferable that the ink composition of the presentinvention comprises neither a silicone-based surfactant nor afluorine-based surfactant or comprises a total content of silicone-basedand fluorine-based surfactants, relative to the total weight of the inkcomposition, of greater than 0 wt % but no greater than 0.1 wt %, andpreferably greater than 0 wt % but no greater than 0.05 wt %.

As a surfactant other than silicone-based and fluorine-basedsurfactants, those described in JP-A-62-173463 and JP-A-62-183457 can becited. Examples thereof include an anionic surfactant such as a dialkylsulfosuccinate salt, an alkylnaphthalene sulfonic acid salt, or a fattyacid salt, a nonionic surfactant such as a polyoxyethylene alkyl ether,a polyoxyethylene alkyl allyl ether, an acetylene glycol, or apolyoxyethylene-polyoxypropylene block copolymer, and a cationicsurfactant such as an alkylamine salt or a quaternary ammonium salt.

(Component F) Colorant

In the present invention, the ink composition may preferably contain acolorant in order to improve the visibility of a formed image area.

The colorant is not particularly limited, but a pigment and anoil-soluble dye that have excellent weather resistance and rich colorreproduction are preferable, and it may be selected from any knowncoloring agent such as a soluble dye. It is preferable that the colorantdoes not function as a polymerization inhibitor in a polymerizationreaction, which is a curing reaction. This is because the sensitivity ofthe curing reaction by actinic radiation should not be degraded.

The pigment that can be used in the present invention is notparticularly limited and, for example, organic and inorganic pigmentshaving the numbers below described in the Color Index may be used.

That is, as a red or magenta pigment, Pigment Red 3, 5, 19, 22, 31, 38,43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1,81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149,166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, or 257,Pigment Violet 3, 19, 23, 29, 30, 37, 50, or 88, and Pigment Orange 13,16, 20, or 36;

as a blue or cyan pigment, Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4,15:6, 16, 17-1, 22, 27, 28, 29, 36, or 60;

as a green pigment, Pigment Green 7, 26, 36, or 50;

as a yellow pigment, Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37,55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 120, 137, 138, 139, 153,154, 155, 157, 166, 167, 168, 180, 185, or 193; as a black pigment,

Pigment Black 7, 28, or 26; as a white pigment,

Pigment White 6, 18, or 21, etc. may be used according to the intendedapplication.

In the present invention, a disperse dye may be used in a range thatenables it to be dissolved in a water-immiscible organic solvent.Disperse dyes generally include water-soluble dyes, but in the presentinvention it is preferable for the disperse dye to be used in a rangesuch that it dissolves in a water-immiscible organic solvent.

Specific preferred examples of the disperse dye include CI DisperseYellow 5, 42, 54, 64, 79, 82, 83, 93, 99, 100, 119, 122, 124, 126, 160,184:1, 186, 198, 199, 201, 204, 224, and 237; CI Disperse Orange 13, 29,31:1, 33, 49, 54, 55, 66, 73, 118, 119, and 163; CI Disperse Red 54, 60,72, 73, 86, 88, 91, 92, 93, 111, 126, 127, 134, 135, 143, 145, 152, 153,154, 159, 164, 167:1, 177, 181, 204, 206, 207, 221, 239, 240, 258, 277,278, 283, 311, 323, 343, 348, 356, and 362; CI Disperse Violet 33; CIDisperse Blue 56, 60, 73, 87, 113, 128, 143, 148, 154, 158, 165, 165:1,165:2, 176, 183, 185, 197, 198, 201, 214, 224, 225, 257, 266, 267, 287,354, 358, 365, and 368; and CI Disperse Green 6:1 and 9

It is preferable that the colorant is added to the ink composition andthen dispersed in the ink to an appropriate degree. For dispersion ofthe colorant, for example, a dispersing machine such as a ball mill, asand mill, an attritor, a roll mill, an agitator, a Henschel mixer, acolloidal mill, an ultrasonic homogenizer, a pearl mill, a wet type jetmill, or a paint shaker may be used.

The colorant may be added directly to the ink composition, but in orderto improve dispersibility it may be added in advance to a solvent or adispersing medium such as a polymerizable compound used in the presentinvention.

In the present invention, in order to avoid the problem of the solventresistance being degraded when the solvent remains in the cured imageand the VOC (Volatile Organic Compound) problem of the residual solvent,it is preferable to add the colorant in advance to a dispersing mediumsuch as a polymerizable compound. As a polymerizable compound used, itis preferable in terms of dispersion suitability to select a monomerhaving the lowest viscosity.

The colorants may be used by appropriately selecting one type or two ormore types according to the intended purpose of the ink composition.

When a colorant such as a pigment that is present as a solid in the inkcomposition is used, it is preferable for the colorant, the dispersant,the dispersing medium, dispersion conditions, and filtration conditionsto be set so that the average particle size of colorant particles ispreferably 0.005 to 0.5 μm, more preferably 0.01 to 0.45 μm, and yetmore preferably 0.015 to 0.4 μm. By such control of particle size,clogging of a head nozzle can be suppressed, and the ink storagestability, the transparency, and the curing sensitivity can bemaintained.

The content of the colorant in the ink composition is appropriatelyselected according to the color and the intended purpose, and ispreferably 0.01 to 30 wt % relative to the weight of the entire inkcomposition.

(Component G) Dispersant

The ink composition of the present invention preferably comprises adispersant. Especially, when the pigment is used, the ink compositionpreferably comprises a dispersant in order to stably disperse thepigment in the ink composition.

As the dispersant that can be used in the present invention, a polymericdispersant is preferable. The ‘polymeric dispersant’ referred to in thepresent invention means a dispersant having a weight-average molecularweight of 1,000 or greater.

Examples of the polymeric dispersant include polymeric dispersants suchas DISPERBYK-101, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106,DISPERBYK-111, DISPERBYK-161, DISPERBYK-162, DISPERBYK-163,DISPERBYK-164, DISPERBYK-166, DISPERBYK-167, DISPERBYK-168,DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, and DISPERBYK-182(manufactured by BYK Chemie), EFKA4010, EFKA4046, EFKA4080, EFKA5010,EFKA5207, EFKA5244, EFKA6745, EFKA6750, EFKA7414, EFKA745, EFKA7462,EFKA7500, EFKA7570, EFKA7575, and EFKA7580 (manufactured by EFKAAdditives), Disperse Aid 6, Disperse Aid 8, Disperse Aid 15, andDisperse Aid 9100 (manufactured by San Nopco Limited); various types ofSOLSPERSE dispersants such as Solsperse 3000, 5000, 9000, 12000, 13240,13940, 17000, 22000, 24000, 26000, 28000, 32000, 36000, 39000, 41000,and 71000 (manufactured by Noveon); Adeka Pluronic L31, F38, L42, L44,L61, L64, F68, L72, P95, F77, P84, F87, P94, L101, P103, F108, L121, andP-123 (manufactured by Adeka Corporation), Ionet S-20 (manufactured bySanyo Chemical Industries, Ltd.), and Disparlon KS-860, 873SN, and 874(polymeric dispersant), #2150 (aliphatic poly carboxylic acid), and#7004 (polyether ester type) (manufactured by Kusumoto Chemicals, Ltd.).

The content of the dispersant in the ink composition of the presentinvention is appropriately selected according to the intended purpose,and is generally preferably 0.05 to 15 wt % relative to the weight ofthe entire ink composition.

(Component H) Oligomer

The ink composition of the present invention preferably comprises anoligomer.

An oligomer is generally a polymer in which a limited number (usually 5to 100) of monomers are bonded, and known compounds called oligomers maybe selected freely, but in the present invention it is preferable toselect a polymer having a weight-average molecular weight of 400 to10,000 (more preferably 500 to 5,000).

The oligomer may have a radically polymerizable group. The radicallypolymerizable group is preferably an ethylenically unsaturated group,and more preferably a (meth)acryloxy group.

The oligomer in the present invention may be any oligomer, and examplesthereof include an olefin-based oligomer (an ethylene oligomer, apropylene oligomer, a butene oligomer, etc.), a vinyl-based oligomer (astyrene oligomer, a vinyl alcohol oligomer, a vinylpyrrolidone oligomer,an acrylate oligomer, a methacrylate oligomer, etc.), a diene-basedoligomer (a butadiene oligomer, a chloroprene rubber, a pentadieneoligomer, etc.), a ring-opening polymerization type oligomer (di-, tri-,tetra-ethylene glycol, polyethylene glycol, polyethylimine, etc.), anaddition-polymerization type oligomer (an oligoester acrylate, apolyamide oligomer, a polyisocyanate oligomer), and anaddition-condensation oligomer (a phenolic resin, an amino resin, axylene resin, a ketone resin, etc.). Among them an oligoester(meth)acrylate is preferable, and among them a urethane (meth)acrylate,a polyester (meth)acrylate, and an epoxy (meth)acrylate are preferable,and a urethane (meth)acrylate is more preferable.

As the urethane (meth)acrylate, an aliphatic urethane (meth)acrylate andan aromatic urethane (meth)acrylate may preferably be cited, and analiphatic urethane (meth)acrylate may more preferably be cited.

Furthermore, the urethane (meth)acrylate is preferably a tetra- orlower-functional urethane (meth)acrylate, and more preferably a di- orlower-functional urethane (meth)acrylate.

In accordance with a urethane (meth)acrylate being contained, an inkcomposition having excellent adhesion to a substrate and excellentcurability is obtained.

With respect to the oligomer, ‘Origomar Handobukku (Oligomer Handbook)’(edited by Junji Furukawa, The Chemical Daily Co., Ltd.) may also bereferred to.

As oligomer commercial products, examples of urethane (meth)acrylatesinclude R1204, R1211, R1213, R1217, R1218, R1301, R1302, R1303, R1304,R1306, R1308, R1901, and R1150 manufactured by Dai-Ichi Kogyo SeiyakuCo., Ltd., the EBECRYL series (e.g. EBECRYL 230, 270, 4858, 8402, 8804,8807, 8803, 9260, 1290, 1290K, 5129, 4842, 8210, 210, 4827, 6700, 4450,and 220) manufactured by Daicel-Cytec Company Ltd., NK Oligo U-4HA,U-6HA, U-15HA, U-108A, and U200AX manufactured by Shin-Nakamura ChemicalCo., Ltd., and Aronix M-1100, M-1200, M-1210, M-1310, M-1600, and M-1960manufactured by Toagosei Co., Ltd.

Examples of polyester (meth)acrylates include the EBECRYL series (e.g.EBECRY L770, IRR467, 81, 84, 83, 80, 675, 800, 810, 812, 1657, 1810,IRR302, 450, 670, 830, 870, 1830, 1870, 2870, IRR267, 813, IRR483, 811,etc.) manufactured by Daicel-Cytec Company Ltd. and Aronix M-6100,M-6200, M-6250, M-6500, M-7100, M-8030, M-8060, M-8100, M-8530, M-8560,and M-9050 manufactured by Toagosei Co., Ltd.

Examples of epoxy (meth)acrylates include the EBECRYL series (e.g.EBECRYL 600, 860, 2958, 3411, 3600, 3605, 3700, 3701, 3703, 3702, 3708,RDX63182, 6040, etc.) manufactured by Daicel-Cytec Company Ltd.

With regard to the oligomer, one type thereof may be used on its own ortwo or more types may be used in combination.

The content of the oligomer in the ink composition of the presentinvention is, relative to the total weight of the ink composition,preferably 0.1 to 50 wt %, more preferably 0.5 to 20 wt %, and yet morepreferably 1 to 10 wt %.

Other Components

The ink composition of the present invention may comprise as necessary,in addition to the above-mentioned components, a co-sensitizer, a UVabsorber, an antioxidant, an antifading agent, a conductive salt, asolvent, a polymer compound, a basic compound, etc. They are describedin JPA-2009-221416 and may be used in the present invention as well.

Furthermore, from the viewpoint of storage properties and suppression ofhead clogging, the ink composition of the present invention preferablycomprises a polymerization inhibitor.

The polymerization inhibitor is preferably added at 200 to 20,000 ppmrelative to the total amount of the ink composition of the presentinvention.

Examples of the polymerization inhibitor include a nitroso-basedpolymerization inhibitor, a hindered amine-based polymerizationinhibitor, hydroquinone, benzoquinone, p-methoxyphenol, TEMPO, TEMPOL,and Al cupferron.

Properties of Ink Composition

In the present invention, the ink composition has a viscosity at 25° C.of preferably no more than 40 mPa·s, more preferably 5 to 40 mPa·s, andyet more preferably 7 to 30 mPa·s. Furthermore, the viscosity of the inkcomposition at the discharge temperature (preferably 25° C. to 80° C.,and more preferably 25° C. to 50° C.) is preferably 3 to 15 mPa·s, andmore preferably 3 to 13 mPa·s. With regard to the ink composition of thepresent invention, it is preferable that its component ratio isappropriately adjusted so that the viscosity is in the above-mentionedrange. When the viscosity at room temperature is set to be high, evenwhen a porous recording medium (support) is used, penetration of the inkcomposition into the recording medium can be prevented, and uncuredmonomer can be reduced. Furthermore, ink spreading when droplets of inkcomposition have landed can be suppressed, and as a result there is theadvantage that the image quality is improved.

The surface tension of the ink composition of the present invention at25° C. is preferably 20 to 35 mN/m, and more preferably 23 to 33 mN/m.When recording is carried out on various types of recording medium suchas polyolefin, PET, coated paper, and uncoated paper, from the viewpointof spread and penetration, it is preferably at least 20 mN/m, and fromthe viewpoint of wettability it is preferably not more than 35 mN/m.

Inkjet Recording Method

The inkjet recording method of the present invention comprises (a) astep of forming an image onto a support by discharging the inkjet inkcomposition of the present invention by way of inkjet method, and, (b) astep of curing the inkjet ink composition and obtaining a printedmaterial having a cured image on the support by irradiating the obtainedimage with actinic radiation. The inkjet recording method of the presentinvention comprises the steps (a) and (b) above and thus forms an imagefrom the ink composition cured on the support.

In the present invention, the support is not particularly limited, andknown recording medium may be used. Examples thereof include paper,paper laminated with a plastic (e.g. polyethylene, polypropylene,polystyrene, etc.), a metal plate (e.g. aluminum, zinc, copper, etc.), aplastic film (e.g. cellulose diacetate, cellulose triacetate, cellulosepropionate, cellulose butyrate, cellulose acetate butyrate, cellulosenitrate, polyethylene terephthalate, polyethylene, polystyrene,polypropylene, polycarbonate, polyvinylacetal, etc.), and paper orplastic film laminated or vapor-deposited with the above metal. In thepresent invention, as the recording medium, a non-absorbing recordingmedium may suitably be used.

An inkjet recording device used in the inkjet recording method of thepresent invention is not particularly limited, and any known inkjetrecording device that can achieve an intended resolution may be used.That is, any known inkjet recording device, such as a commercialproduct, may be used in order to discharge an ink composition onto asupport in step (a) of the inkjet recording method of the presentinvention.

The inkjet recording device that can be used in the present invention isequipped with, for example, an ink supply system, a temperature sensor,and an actinic radiation source.

The ink supply comprises, for example, a main tank containing the inkcomposition of the present invention, a supply pipe, an ink compositionsupply tank immediately before an inkjet head, a filter, and a piezosystem inkjet head. The piezo system inkjet head may be driven so as todischarge a multisize dot of preferably 1 to 100 μL, more preferably 3to 42 μL, and yet more preferably 8 to 30 μL, at a resolution ofpreferably 320×320 to 4,000×4,000 dpi, more preferably 400×400 to1,600×1,600 dpi, and yet more preferably 720×720 dpi. Here, dpi referredto in the present invention means the number of dots per 2.54 cm.

In the present invention, since it is desirable for the ink compositionto be discharged at a constant temperature, a section from the inkcomposition supply tank to the inkjet head is thermally insulated andheated. A method of controlling temperature is not particularly limited,but it is preferable to provide, for example, temperature sensors at aplurality of pipe section positions, and control heating according tothe ink composition flow rate and the temperature of the surroundings.The temperature sensors may be provided on the ink composition supplytank and in the vicinity of the inkjet head nozzle. Furthermore, thehead unit that is to be heated is preferably thermally shielded orinsulated so that the device main body is not influenced by thetemperature of the outside air. In order to reduce the printer start-uptime required for heating, or in order to reduce the thermal energyloss, it is preferable to thermally insulate the head unit from othersections and also to reduce the heat capacity of the entire heated unit.

The radiation curing type ink composition such as the ink composition ofthe present invention generally has a viscosity that is higher than thatof a normal ink composition or a water-based ink composition used for aninkjet recording ink composition, and variation in viscosity due to achange in temperature at the time of discharge is large. Viscosityvariation in the ink composition has a large effect on changes in liquiddroplet size and changes in liquid droplet discharge speed and,consequently, causes the image quality to be degraded. It is thereforenecessary to maintain the ink composition discharge temperature asconstant as possible. In the present invention, the control range forthe temperature of ink composition is preferably ±5° C. of a settemperature, more preferably ±2° C. of the set temperature, and yet morepreferably ±1° C. of the set temperature.

The curing step (b) of irradiating the image thus obtained with actinicradiation so as to cure the inkjet ink composition and obtain a printedmaterial having the image cured on the support are explained.

The ink composition discharged onto the recording medium cures uponexposure to actinic radiation. This is due to a initiating species suchas a radical being generated by decomposition of the photopolymerizationinitiator contained in the ink composition of the present invention byirradiation with actinic radiation, the initiating species functioningso as to make a polymerization reaction of a radically polymerizablecompound take place and to promote it. In this process, if a sensitizeris present together with the polymerization initiator in the inkcomposition, the sensitizer in the system absorbs actinic radiation,becomes excited, and promotes decomposition of the polymerizationinitiator by contact with the polymerization initiator, thus enabling acuring reaction with higher sensitivity to be achieved.

The actinic radiation used in this process may include α rays, γ rays,an electron beam, X rays, UV rays, visible light, and IR rays. Althoughit depends on the absorption characteristics of the sensitizing dye, thepeak wavelength of the actinic radiation is, for example, 200 to 600 nm,preferably 300 to 450 nm, and more preferably 350 to 420 nm.

Furthermore, in the present invention, the photopolymerizationinitiation system has sufficient sensitivity for low output actinicradiation. The actinic radiation is applied therefore so that theillumination intensity on the exposed surface is, for example, 10 to4,000 mW/cm², and preferably 20 to 2,500 mW/cm².

As an actinic radiation source, a mercury lamp, a gas/solid laser, etc.are mainly used, and for UV photocuring inkjet ink composition a mercurylamp and a metal halide lamp are widely known. However, from theviewpoint of protection of the environment, there has recently been astrong desire for mercury not to be used, and replacement by a GaNsemiconductor UV light emitting device is very useful from industrialand environmental viewpoints. Furthermore, LEDs (UV-LED) and LDs (UV-LD)have small dimensions, long life, high efficiency, and low cost, andtheir use as a photocuring inkjet light source can be expected.

Furthermore, light-emitting diodes (LED) and laser diodes (LD) may beused as the source of actinic radiation. In particular, when a UV raysource is needed, a UV-LED or a UV-LD may be used. For example, NichiaCorporation has marketed a violet LED having a wavelength of the mainemission spectrum of between 365 nm and 420 nm. Furthermore, when ashorter wavelength is needed, the example of the LED includes a LED,disclosed in U.S. Pat. No. 6,084,250, that can emit actinic radiationwhose wavelength is centered between 300 nm and 370 nm. Furthermore,another violet LED is available, and irradiation can be carried out withradiation of a different UV bandwidth. The actinic radiation sourcepreferable in the present invention is a UV-LED, and a UV-LED having apeak wavelength at 350 to 420 nm is particularly preferable.

The maximum illumination intensity of the LED on a recording medium ispreferably 10 to 2,000 mW/cm², more preferably 20 to 1,000 mW/cm², andparticularly preferably 50 to 800 mJ/cm².

The ink composition of the present invention is desirably exposed tosuch actinic radiation for preferably 0.01 to 120 sec., more preferably0.01 to 90 sec., and yet more preferably 0.01 to 10 sec.

And in the present invention, it is desirable for the ink composition tobe cured by irradiated for 0.01 to 10 sec. with actinic radiation andwith no greater than 2,000 mW/cm² of illumination intensity afterdischarging the ink composition.

Irradiation conditions and a basic method for irradiation with actinicradiation are disclosed in JP-A-60-132767. Specifically, a light sourceis provided on either side of a head unit that includes an inkcomposition discharge device, and the head unit and the light source aremade to scan by a so-called shuttle system. Irradiation with actinicradiation is carried out after a certain time (preferably 0.01 to 0.5sec., more preferably 0.01 to 0.3 sec., and particularly preferably 0.01to 0.15 sec.) has elapsed from when the ink composition has landed. Bycontrolling the time from ink composition landing to irradiation so asto be a minimum in this way, it becomes possible to prevent the inkcomposition that has landed on a recording medium from spreading beforebeing cured. Furthermore, since the ink composition can be exposedbefore it reaches a deep area of a porous recording medium that thelight source cannot reach, it is possible to prevent monomer fromremaining unreacted.

Furthermore, curing may be completed using another light source that isnot driven. WO99/54415 discloses, as an irradiation method, a methodemploying an optical fiber and a method in which a collimated lightsource is incident on a mirror surface provided on a head unit sideface, and a recorded area is irradiated with UV light.

In the inkjet recording method of the present invention, it ispreferable to form at least part of an image in a printed material byrepeating two or more times the image formation step (a) and the curingstep (b) since an image having excellent surface gloss is obtained.

Examples of the mode in which at least part of an image in a printedmaterial is formed by repeating two or more times the image formationstep (a) and the curing step (b) include a mode in which a color imageis formed by carrying out the steps (a) and (b) once per color, a modein which a single color image is formed by repeating the steps (a) and(b) two or more times for the single color image, and a mode in which acolor image is formed by repeating the steps (a) and (b) two or moretimes for one color of the color image to form a single color image andfurther repeating the steps (a) and (b) two or more times in the samemanner for another color of the color image.

The ink composition of the present invention preferably contains neithera silicone-based surfactant nor a fluorine-based surfactant. Whenrepeating the steps (a) and (b) two or more times using the inkcomposition not containing these surfactants, these surfactants are notlocalized on the surface of a previously discharged ink compositionliquid droplet, the fired droplet surface is kept in a liquid state fora long period of time, coalescing with a subsequently discharged inkcomposition liquid droplet therefore easily proceeds, and as a resultthe surface gloss of an image improves.

By employing such a inkjet recording method as described above, it ispossible to maintain a uniform dot diameter for landed ink compositioneven for various types of support having different surface wettability,thereby improving the image quality. In order to obtain a color image,it is preferable to superimpose colors in order from those with a highlightness. By superimposing ink compositions in order from one with highlightness, it is easy for radiation to reach a lower ink composition,the curing sensitivity is good, the amount of residual monomerdecreases, and an improvement in adhesion can be expected. Furthermore,although it is possible to discharge all colors and then expose them atthe same time, it is preferable to expose one color at a time from theviewpoint of promoting curing.

The inkjet recording method of the present invention may suitably employthe ink set comprising at least one ink composition of the presentinvention. The order in which colored ink compositions are discharged isnot particularly limited, but it is preferable to apply to a recordingmedium from a colored ink composition having a high lightness; when theink compositions of yellow, cyan, magenta, and black are used, they arepreferably applied on top of the recording medium in the orderyellow→cyan→magenta→black. Furthermore, when white is additionally used,they are preferably applied on top of the recording medium in the orderwhite→yellow→cyan→magenta→black. Moreover, the present invention is notlimited thereto, and an ink set comprising a total of seven colors, thatis, light cyan, light magenta ink compositions and cyan, magenta, black,white, and yellow dark ink compositions may preferably be used, and inthis case they are applied on top of the recording medium in the orderwhite→light cyan→light magenta→yellow→cyan→magenta→black.

In this way, the ink composition of the present invention may be curedby irradiation with actinic radiation in high sensitivity and form animage on the surface of the support.

When using as an ink set comprising plurality of ink compositions havinga different color, the ink set is not particularly limited as long as itis an ink set having two or more types of ink compositions incombination, the ink set comprising in combination at least one inkcomposition of the present invention and another ink composition of thepresent invention or an ink composition other than one of the presentinvention, and it is preferable for the ink set to comprise at least oneink composition of the present invention having a color selected fromcyan, magenta, yellow, black, white, light magenta, and light cyan.

Furthermore, the ink set of the present invention may be suitably usedin the inkjet recording method of the present invention.

In order to obtain a full color image using the ink composition of thepresent invention, it is preferable to use, as the ink set of thepresent invention, an ink set comprising at least four dark inkcompositions of yellow, cyan, magenta, and black, it is more preferableto use an ink set comprising in combination five dark ink compositionsof yellow, cyan, magenta, black, and white and at least one inkcomposition of the present invention, and it is yet more preferable touse an ink set comprising in combination five dark ink compositions ofyellow, cyan, magenta, black, and white and two, that is, light cyan,and light magenta ink compositions.

The ‘dark ink composition’ referred to in the present invention means anink composition for which the content of the colorant exceeds 1 wt % ofthe entire ink composition. The colorant is not particularly limited; aknown colorant may be used, and examples thereof include a pigment and adisperse dye.

The ink set of the present invention may comprise at least one dark inkcomposition and at least one light ink composition. The dark inkcomposition and the light ink composition employ colorants of similarcolors, the ratio of the colorant concentration of the dark inkcomposition to the colorant concentration of the light ink compositionis preferably dark ink composition:light ink composition=15:1 to 4:1,more preferably 12:1 to 4:1, and yet more preferably 10:1 to 4.5:1. Whenthe ratio is in the above-mentioned range, a vivid full color image withlittle feeling of grain can be obtained.

In accordance with the present invention, there can be provided aninkjet ink composition that has excellent curability and gives an imagefree from stripe unevenness and having excellent surface gloss andflexibility, and an inkjet recording method that has excellentcurability and gives an image free from stripe unevenness and havingexcellent surface gloss and flexibility.

EXAMPLES

The present invention is explained below more specifically by referenceto Examples and Comparative Examples. However, the present inventionshould not be construed as being limited by these Examples. ‘Parts’ inthe description below means ‘parts by weight’ unless otherwisespecified.

Materials used in the present invention are as follows.

Colorants

IRGALITE BLUE GLVO (cyan pigment, Ciba Specialty Chemicals)CINQUASIA MAGENTA RT-355-D (magenta pigment, Ciba Specialty Chemicals)NOVOPERM YELLOW H2G (yellow pigment, Clariant)SPECIAL BLACK 250 (black pigment, Ciba Specialty Chemicals)TIPAQUE CR60-2 (white pigment, Ishihara Sangyo Kaisha Ltd.)

Dispersants

SOLSPERSE 32000 (dispersant, Noveon)SOLSPERSE 36000 (dispersant, Noveon)

Component A V-CAP (N-vinylcaprolactam, ISP Inc.) Component B

NK Ester A-NOD-N (1,9-nonanediol diacrylate, Shin-Nakamura Chemical Co.,Ltd.)CD595 (1,10-decanediol diacrylate, Sartomer)CD262 (1,12-dodecanediol diacrylate, Sartomer)CD406 (cyclohexanedimethanol diacrylate, Sartomer)SR341 (3-methyl-1,5-pentanediol diacrylate, Sartomer)

Component C

IRGACURE 369 (photopolymerization initiator,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, Ciba-GeigyLtd.)IRGACURE 819 (photopolymerization initiator,bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, Ciba-Geigy Ltd.)SPEEDCURE ITX (photopolymerization initiator, isopropylthioxanthone, LAMBSON)Compound I-14 (photopolymerization initiator, compound below)

Other Polymerizable Compounds

NK Ester AMP-10G (phenoxyethyl acrylate, Shin-Nakamura Chemical Co.,Ltd.)SR9003 (PO-modified neopentyl glycol diacrylate, Sartomer)SR508 (dipropylene glycol diacrylate, Sartomer)CD217 (4-t-butylcyclohexyl acrylate, Sartomer)CD420 (3,3,5-trimethylcyclohexyl acrylate, Sartomer)SR238 (1,6-hexanediol diacrylate, Sartomer)SR506D (isobornyl acrylate, Sartomer)SR440 (isooctyl acrylate, Sartomer)SR395 (isodecyl acrylate, Sartomer)SR833S (tricyclodecanedimethanol diacrylate, Sartomer)KAYARAD R-684 (dicyclopentanyl diacrylate, Nippon Kayaku Co., Ltd.)

Other Polymerization Initiators

LUCIRIN TPO (photopolymerization initiator,2,4,6-trimethylbenzoyldiphenylphosphine oxide, BASF)IRGACURE 184 (photopolymerization initiator, 1-hydroxycyclohexyl phenylketone, Ciba-Geigy Ltd.)IRGACURE 127 (photopolymerization initiator,2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methylpropan-1-one,Ciba-Geigy Ltd.)

Oligomer

CN964 A85 (difunctional aliphatic urethane acrylate containing 15 wt %tripropylene glycol diacrylate, Sartomer)

Polymerization Inhibitor

FIRSTCURE ST-1 (polymerization inhibitor, mixture oftris(N-nitroso-N-phenylhydroxyamine) aluminum salt (10 wt %) andphenoxyethyl acrylate (90 wt %), Chem First Corporation)

Surfactants

TEGORAD 2100 (silicone-based surfactant, Degussa)BYK-377 (silicone-based surfactant, BYK Chemie)

Preparation of Each Mill Base

300 parts by weight of IRGALITE BLUE GLVO, 620 parts by weight ofSR9003, and 80 parts by weight of SOLSPERSE 32000 were mixed bystirring, thus giving cyan mill base A. Preparation of cyan mill base Awas carried out by dispersing using a Motor Mill M50 disperser (EigerMachinery, Inc.) with zirconia beads having a diameter of 0.65 mm at aperipheral speed of 9 m/s for 4 hours.

Magenta mill base B, yellow mill base C, black mill base D, and whitemill base E were also prepared in the same manner as for cyan mill baseA using compositions and dispersion conditions shown in Table 1.

TABLE 1 Mill base Cyan Magenta Yellow Black White mill mill mill millmill base A base B base C base D base E Composition IRGALITE BLUE GLVO300 — — — — (parts) CINQUASIA MAGENTA — 300 — — — RT-355 D NOVOPERMYELLOW H2G — — 300 — — SPECIAL BLACK 250 — — — 400 — TIPAQUE CR60-2 — —— — 500 SR9003 620 600 600 520 440 SOLSPERSE 32000  80 100 100  80  60Dispersion Peripheral speed (m/s)   9   9   9   9   9 conditions Time(hours)   4  10  10   7   4

Examples 1 to 24 and Comparative Examples 1 to 8 Method for PreparingInk Composition

Each ink composition was obtained by mixing and stirring the materialsdescribed in Tables 2 to 7.

Inkjet Recording Method

An inkjet image was printed using a LUXELJET UV250 UV-curing type inkjetprinter (Fujifilm Graphic Systems).

A 100% solid image was printed on Avery Permanent 400 (polyvinylchloride (PVC) support, Avery Dennison Corporation) at a resolution of600×450 dpi with a size of 2 m×1 m. This equipment carried out printingby operating an inkjet head; opposite ends of the head were eachequipped with one UV lamp, and irradiation was carried out from the twoUV lamps in one head operation. A solid image was formed by alternatelyrepeating ink droplet firing and UV irradiation with the two lamps eighttimes for the same position of the support. A lamp was equipped with aSUB ZERO 085 H bulb lamp unit manufactured by Integration Technology,and front and rear lamp intensity was set at level 3.

During printing, when the exposure area illumination intensity wasmeasured, it was found to be 980 mW/cm². Furthermore, the time fromdischarge until exposure was 0.2 to 0.3 sec. The amount discharged perdrop was in the range of 6 to 42 μL.

Evaluation of Surface Gloss

Measurement was carried out for an image obtained by the above-mentionedinkjet recording method using a surface gloss meter manufactured bySheen Instruments Ltd. at a measurement angle of 60°. The evaluationcriteria were as follows.

5: a surface gloss of at least 504: a surface gloss of at least 40 but less than 503: a surface gloss of at least 30 but less than 402: a surface gloss of at least 20 but less than 301: a surface gloss of less than 20

Evaluation of Image Stripe Unevenness

Stripe unevenness of an image obtained by the above-mentioned inkjetimage recording method was evaluated visually from a position 1.5 m awayfrom the image. The evaluation criteria were as follows.

3: stripe unevenness could not be clearly identified visually.2: slight stripe unevenness could be identified visually.1: stripe unevenness could be clearly identified visually.

Evaluation of Curability

The degree of tackiness of an image obtained by the above-mentionedinkjet recording method was evaluated using the criteria below by touch.

3: there was no tackiness on the image.2: the image was slightly tacky, but uncured ink composition or curedfilm did not transfer to the hand.1: the image was tacky, and some uncured ink composition or cured filmtransferred to the hand.

Evaluation Method for Flexibility: Bending Test

As a method for evaluating the flexibility of a cured film, a bendingtest was carried out.

100% and 200% solid images were formed by the above-mentioned inkjetrecording method and evaluation was carried out using the criteriabelow.

3: no cracks occurred for 100% and 200% samples.2: no cracks occurred for the 100% sample, but cracks occurred in thebent part of an image area for the 200% average film thickness sample.1: cracks occurred in the bent part of an image area for both 100% and200% average film thickness samples.

TABLE 2 Example Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Color ofink composition Cyan Magenta Yellow Black White Cyan Cyan Cyan PigmentCyan pigment 2.46 — — — — 2.46 2.46 2.46 Magenta pigment — 5.4 — — — — —— Yellow pigment — — 3.75 — — — — — Black pigment — — — 3.6 — — — —White pigment — — — — 15 — — — Dispersant SOLSPERSE 32000 0.656 1.8 1.250.72 — 0.656 0.656 0.656 SOLSPERSE 36000 — — — — 1.8 — — — Mono- Compo-N-Vinylcaprolactam 24 24 24 24 16 24 24 24 mer nent (A) Compo-Cyclohexane- — — — — — 40.6 — — nent (B) dimethanol diacrylate3-Methyl-1,5- 40.6 38 36 40.5 35.45 — — — pentanediol diacrylate1,9-Nonanediol — — — — — — 40.6 — diacrylate 1,10-Decanediol — — — — — —— 40.6 diacrylate Other Phenoxyethyl acrylate 10.25 10.15 17.65 8.65 —10.25 10.25 10.25 monomer PO-modified 5.084 10.8 7.5 4.68 13.2 5.0845.084 5.084 neopentyl glycol diacrylate Oligomer CN964 A85 8 2 2 8 — 8 88 Polymerization FIRSTCURE ST-1 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05inhibitor (Al salt only) Poly- Compo- IRUGACURE 369 1 1 1 2 — 1 1 1meri- nent (C) IRGACURE 819 4.9 4.8 4.8 4.8 — 4.9 4.9 4.9 zation I-14 —— — — 5 — — — initiator ITX 3 2 2 3 — 3 3 3 Other IRGACURE 184 — — — —9.5 — — — polymeri- LUCIRIN TPO — — — — 4 — — — zation initiator Total(parts by weight) 100 100 100 100 100 100 100 100 Performance Surfacegloss 4 4 4 4 4 4 2 3 evaluation results Image stripe unevenness 3 3 3 33 3 3 3 Curability 3 3 3 3 3 3 3 3 Flexibility 3 3 3 3 3 3 3 3

TABLE 3 Example Ex. 1 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15Color of ink composition Cyan Cyan Cyan Cyan Cyan Cyan Cyan Cyan PigmentCyan pigment 2.46 2.46 2.46 2.46 2.46 2.46 2.46 2.46 DispersantSOLSPERSE 32000 0.656 0.656 0.656 0.656 0.656 0.656 0.656 0.656 Mono-Compo- N-Vinylcaprolactam 24 24 24 24 24 24 24 24 mer nent (A) Compo-3-Methyl-1,5- 40.6 — 30.6 25.6 20.6 15.6 40.6 40.6 nent (B) pentanedioldiacrylate 1,12- — 40.6 — — — — — — Dodecanediol diacrylate OtherPhenoxyethyl 10.25 10.25 10.25 10.25 10.25 10.25 10.2 10.15 monomeracrylate PO-modified 5.084 5.084 5.084 5.084 5.084 5.084 5.084 5.084neopentyl glycol diacrylate Dipropylene — — 10 15 20 25 — — glycoldiacrylate Oligomer CN964 A85 8 8 8 8 8 8 8 8 Polymerization FIRSTCUREST-1 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 inhibitor (Al salt only)Poly- Compo- IRGACURE 369 1 1 1 1 1 1 1 1 meri- nent (C) IRGACURE 8194.9 4.9 4.9 4.9 4.9 4.9 4.9 4.9 zation ITX 3 3 3 3 3 3 3 3 initiatorSurfactant TEGORAD 2100 — — — — — — 0.05 0.1 Total (parts by weight) 100100 100 100 100 100 100 100 Performance Surface gloss 4 3 4 3 3 2 2 2evaluation Image stripe 3 3 3 3 3 3 3 3 results unevenness Curability 33 3 3 3 3 3 3 Flexibility 3 3 3 3 3 3 3 3

TABLE 4 Example Ex. 1 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Ex. 20 Color of inkcomposition Cyan Cyan Cyan Cyan Cyan Cyan Pigment Cyan pigment 2.46 2.462.46 2.46 2.46 2.46 Dispersant SOLSPERSE 32000 0.656 0.656 0.656 0.6560.656 0.656 Mono- Compo- N-Vinylcaprolactam 24 24 24 24 24 24 mer nent(A) Compo- 3-Methyl-1,5-pentanediol 40.6 31.5 31.5 20.5 23.35 40.6 nent(B) diacrylate Other Phenoxyethyl acrylate 10.25 — — — — 10.25 monomerPO-modified neopentyl 5.084 5.084 5.084 5.084 5.084 5.084 glycoldiacrylate 4-t-Butylcyclohexyl acrylate — 19.35 — 30.35 — —3,3,5-Trimethylcyclohexyl — — 19.35 — — — acrylate Isodecyl acrylate — —— — 15 — Tricyclodecanedimethanol — — — — 12.5 — diacrylate OligomerCN964 A85 8 8 8 8 8 8 Polymerization FIRSTCURE ST-1 0.05 0.05 0.05 0.050.05 0.05 inhibitor (Al salt only) Poly- Compo- IRUGACURE 369 1 1 1 1 1— meri- nent (C) IRGACURE 819 4.9 4.9 4.9 4.9 4.9 — zation I-14 — — — —— — initiator ITX 3 3 3 3 3 3 Other IRGACURE 184 — — — — — 3 polymeri-LUCIRIN TPO — — — — — 9.5 zation initiator Total (parts by weight) 100100 100 100 100 106.6 Performance Surface gloss 4 5 5 5 5 4 evaluationresults Image stripe unevenness 3 3 3 3 3 3 Curability 3 3 3 3 3 3Flexibility 3 3 3 3 3 3

TABLE 5 Example Ex. 1 Ex. 21 Ex. 22 Ex. 23 Ex. 24 Color of inkcomposition Cyan Cyan Cyan Cyan Cyan Pigment Cyan pigment 2.46 2.46 2.462.46 2.46 Dispersant SOLSPERSE 32000 0.656 0.656 0.656 0.656 0.656Monomer Compo- N-Vinylcaprolactam 24 24 24 24 24 nent (A) Compo-3-Methyl-1,5-pentanediol 40.6 40.6 40.6 40.6 40.6 nent (B) diacrylateOther Phenoxyethyl acrylate 10.25 10.25 10.25 10.25 10.25 monomerPO-modified neopentyl 5.084 5.084 5.084 5.084 5.084 glycol diacrylateOligomer CN964 A85 8 8 8 8 8 Polymerization FIRSTCURE ST-1 0.05 0.050.05 0.05 0.05 inhibitor (Al salt only) Polymeri- Compo- IRUGACURE 369 12 1.5 1.5 — zation nent (C) IRGACURE 819 4.9 4.9 4.9 — — initiator I-14— — 5.5 — — ITX 3 — — — 1.5 Other IRGACURE 184 — 3 — 3 3 polymeri-LUCIRIN TPO — — — 9.5 9.5 zation initiator Total (parts by weight) 100101 103 105.1 105.1 Performance Surface gloss 4 4 4 3 3 evaluationresults Image stripe unevenness 3 3 3 3 3 Curability 3 3 3 3 3Flexibility 3 3 3 3 3

TABLE 6 Comparative Example Example Comp. Comp. Comp. Comp. Ex. 1 Ex. 1Ex. 2 Ex. 3 Ex. 4 Color of ink composition Cyan Cyan Cyan Cyan CyanPigment Cyan pigment 2.46 2.46 2.46 2.46 2.46 Dispersant SOLSPERSE 320000.656 0.656 0.656 0.656 0.656 Mono- Component N-Vinylcaprolactam 24 — 2424 24 mer (A) Component 3-Methyl-1,5-pentanediol 40.6 45.08 — — 40.6 (B)diacrylate Other Phenoxyethyl acrylate 10.25 — 50.85 — 6.65 monomerPO-modified neopentyl 5.084 5.084 5.084 5.084 5.084 glycol diacrylateDipropylene glycol — 29.77 — 50.85 — diacrylate Oligomer CN964 A85 8 8 88 8 Polymerization FIRSTCURE ST-1 0.05 0.05 0.05 0.05 0.05 inhibitor (Alsalt only) Poly- Component IRGACURE 369 1 1 1 1 — meri- (C) IRGACURE 8194.9 4.9 4.9 4.9 — zation ITX 3 3 3 3 — initiator Other IRGACURE 184 — —— — 3 polymeri- LUCIRIN TPO — — — — 9.5 zation initiator SurfactantBYK377 Total (parts by weight) 100 100 100 100 100 Performance Surfacegloss 4 2 1 1 2 evaluation results Image stripe unevenness 3 1 1 1 2Curability 3 3 3 3 3 Flexibility 3 2 3 1 3

TABLE 7 Comparative Example Example Comp. Comp. Comp. Comp. Ex. 1 Ex. 5Ex. 6 Ex. 7 Ex. 8 Color of ink composition Cyan Cyan Cyan Cyan CyanPigment Cyan pigment 2.46 2.46 2.46 2.46 2.46 Dispersant SOLSPERSE 320000.656 0.656 0.656 0.656 0.656 Mono- Component N-Vinylcaprolactam 24 1720 5 10 mer (A) Component 3-Methyl-1,5-pentanediol 40.6 — — — — (B)diacrylate Other Phenoxyethyl acrylate 10.25 — — 8 42.75 monomerPO-modified neopentyl 5.084 5.084 5.084 5.084 5.084 glycol diacrylateIsooctyl acrylate — — — 22 — Tridecyl acrylate — — 30 — —Dicyclopentanyl diacrylate — — — — 10 1,6-Hexanediol diacrylate — 27 —7.75 — Isobornyl acrylate — 24.2 — 20 10 Dipropylene glycol diacrylate —15.2 24.25 — — Oligomer CN964 A85 8 — 8 18 — Polymerization FIRSTCUREST-1 0.05 0.05 0.05 0.05 0.05 inhibitor (Al salt only) Poly- ComponentIRGACURE 369 1 — 2 2 2 meri- (C) IRGACURE 819 4.9 — — 6 6 zation ITX 31.2 2 1 1 initiator Other IRGACURE 184 — 1.6 — 2 5 polymeri- IRGACURE127 — — — — 5 zation LUCIRIN TPO — 5.15 5.5 — — initiator SurfactantBYK377 — 0.4 — — — Total (parts by weight) 100 100 100 100 100Performance Surface gloss 4 2 1 2 1 evaluation results Image stripeunevenness 3 1 1 1 2 Curability 3 3 2 3 3 Flexibility 3 3 3 3 3

1. An inkjet ink composition comprising: (Component A) an N-vinyllactam;(Component B) a di(meth)acrylate ester of at least one type of diolselected from the group consisting of a straight-chain hydrocarbon diolhaving 9 to 18 carbon atoms, a branched hydrocarbon diol having 6 to 18carbon atoms, and a monoalicyclic hydrocarbon diol having 6 to 18 carbonatoms; and (Component C) at least one type of polymerization initiatorselected from the group consisting of an α-amino ketone compound, athioxanthone compound, a thiochromanone compound, and a bisacylphosphineoxide compound.
 2. The inkjet ink composition according to claim 1,wherein Component B above is a di(meth)acrylate ester of at least onetype of diol selected from the group consisting of a straight-chainhydrocarbon diol having 10 to 18 carbon atoms, a branched hydrocarbondiol having 6 to 18 carbon atoms, and a monoalicyclic hydrocarbon diolhaving 6 to 18 carbon atoms.
 3. The inkjet ink composition according toclaim 1, wherein Component B above is a di(meth)acrylate ester of atleast one type of diol selected from the group consisting of a branchedhydrocarbon diol having 6 to 18 carbon atoms and a monoalicyclichydrocarbon diol having 6 to 18 carbon atoms.
 4. The inkjet inkcomposition according to claim 2, wherein Component B above is at leastone di(meth)acrylate ester selected from the group consisting of1,10-decanediol diacrylate, 1,12-dodecanediol diacrylate,3-methyl-1,5-pentanediol diacrylate, and cyclohexanedimethanoldiacrylate.
 5. The inkjet ink composition according to claim 3, whereinComponent B above is at least one di(meth)acrylate ester selected fromthe group consisting of 3-methyl-1,5-pentanediol diacrylate andcyclohexanedimethanol diacrylate.
 6. The inkjet ink compositionaccording to claim 1, wherein Component B above comprises3-methyl-1,5-pentanediol diacrylate.
 7. The inkjet ink compositionaccording to claim 1, wherein the inkjet ink composition furthercomprises (Component D) a compound represented by Formula (D),

wherein R¹ denotes a hydrogen atom or a methyl group and R² to R¹²independently denote a hydrogen atom or an alkyl group.
 8. The inkjetink composition according to claim 7, wherein Component D abovecomprises 4-t-butylcyclohexyl (meth)acrylate and/or3,3,5-trimethylcyclohexyl (meth)acrylate.
 9. The inkjet ink compositionaccording to claim 1, wherein Component B above has a content of atleast 15 wt % but no greater than 50 wt % relative to the total weightof the ink composition.
 10. The inkjet ink composition according toclaim 1, wherein Component A above has a content of at least 8 wt % butno greater than 35 wt % relative to the total weight of the inkcomposition.
 11. The inkjet ink composition according to claim 1,wherein the inkjet ink composition comprises at least three types ofpolymerization initiators selected from the group consisting of anα-amino ketone compound, a thioxanthone compound, a thiochromanonecompound, a bisacylphosphine oxide compound, an α-hydroxy ketonecompound, and a monoacylphosphine oxide compound.
 12. The inkjet inkcomposition according to claim 1, wherein the inkjet ink compositioncomprises neither a silicone-based surfactant nor a fluorine-basedsurfactant or comprises a total content of silicone-based andfluorine-based surfactants of greater than 0 wt % but no greater than0.1 wt % relative to the total weight of the ink composition.
 13. Theinkjet ink composition according to claim 1, wherein at least 75 wt % ofethylenically unsaturated compounds contained in the ink composition arecompounds having no ether bond.
 14. An inkjet recording methodcomprising: (a) an image formation step of forming an image above asupport by discharging the inkjet ink composition according to claim 1by an inkjet method; and (b) a curing step of curing the ink compositionby irradiating the obtained image with actinic radiation to thus obtaina printed material having a cured image above the support.
 15. Theinkjet recording method according to claim 14, wherein at least part ofthe image in the printed material is formed by repeating the imageformation step and the curing step two or more times.